1. Field of the Invention
This invention relates to metal doors and particularly to a two piece door construction having two pans that are latched together to form the shell of the door with a core inside.
2. Description of Related Art
Steel doors are typically formed with a metal shell usually having a core inside which may be made of wood or a dense foam such as polyurethane. The steel door shell is typically formed of front and panel members with edge parts or channels therebetween to give the door strength and durability during use and stability during the assembly process. The face plates or panel members of the door have been typically secured by fasteners, such as rivets or screws, or by spot welds. Metal doors have been formed by a pair of telescoping parts locked together by the snap action of latches, avoiding the use of bolts, rivets and welding.
Typical examples of these prior art metal doors are disclosed in U.S. Pat. No. 1,848,715 to Hart and U.S. Pat. and U.S. Pat. No. 4,589,240 to Kendall. However, these constructions have side edges of the door which are interrupted by the latches such that a sufficiently large continuous, smooth metal surface is not provided for the dead bolt and latch preparations or for the hinges. Further, an effective mechanism for properly aligning the panels and maintaining them in an aligned position is not provided.
U.S. Pat. No. 4,896,458, entitled "Door System With Interlocking Panels" to McKann, discloses a door formed by latch and hinge panels which can be attached without fasteners or welding. Each of the panels is formed of a unitary piece of sheet metal and includes a rectangular face member, a side flange extending substantially perpendicularly from the face member along one of its side edges, a first latch formed along a free lateral edge of the side flange remote from the face member, a second latch formed along the opposite side edge of the face member and end flanges extending substantially perpendicularly from the face member along the end edges. The first latch of each panel is secured to the second latch of the other panel such that the panels are secured and form the door, with latches being located at diametrically opposite corners of the door. The McKann patent provides upper and lower end flanges on front and back panels which abut each other and have retaining means comprising projections on one flange of each of the mating flange sets and corresponding mating openings on the other. Tabs are folded against and overlie inner portions of the end flanges to ensure proper alignment of the two panels. The problem with this design is that there is a lack of torsional rigidity because the flanges are not well secured. The need for tabs to prevent lateral shifting of the panels to help hold the door edges formed by side flanges square with the door faces indicates the insufficiency of this design. The alternative retaining means stakes each tab and further indicates the problem of lateral shifting of the panels. But neither design takes into account the twisting of the panels between the upper set and lower set of flanges.
Torsional rigidity with respect to a central axis normal to the front and back of the rectangular door assembly is a common problem of the snap together latching door designs. The problem is particularly acute during the manufacturing and fabrication of the door during which the latched panels are moved from location to location and cutouts are made.